1. Field of the Invention
This invention relates to a light emitting apparatus for use as a light source, a light modulator and the like suitable for optical communications, especially, parallel and large capacity optical transmission between electric circuit elements and the like and which have extremely high light emission efficiency, and, more particularly, to light emitting devices utilizing cavity quantum electrodynamics.
2. Related Background Art
In recent years, technologies for linking the electric circuits using light are expected to overcome the signal delay due to capacitances resulting from electric distribution wires in the large scale integration (LSI), etc. For the purposes of electric linkage, semiconductor lasers have been utilized as light emitting devices. However, the semiconductor laser generally requires a very large injection current density. As a result, integration of many semiconductor lasers on a common substrate causes problems of overheating in the elements and of degraded reliability. As a result, the semiconductor laser is not believed to be suitable as a light emitting device for light transmission between proximate electric circuits.
To solve these problems, there have been developed field-effect type light emission devices having quantum well structures, as is disclosed, for example, in JJAP., vol. 22, pp. L22-L24 (1982). In these devices, the modulation of the number of carriers, done in conventional elements, is not performed, and instead the light emission or radiation rate itself is modulated by spatially separating electrons from holes due to an electric field applied perpendicularly to a quantum well active layer. Therefore, high-speed switching operation is achieved, which is unrelated to the recombination life time of carriers that has been limiting the switching time of the conventional light emitting devices.
Thus, if the above device is utilized as the above-mentioned light emitting device for optical linkage, such optical signal switching becomes possible at very high speed of the order of 10 psec although the injection current density is extremely low. For instance, in the case where a multiplicity of such light emitting devices are arranged on a common substrate, it will be expected that heat generation is low. At the same time excellent characteristics are obtained with respect to the uniformity of light emission and the reliability of the device compared with semiconductor lasers.
However, in the prior art field-effect type light emitting device having quantum well, the depth of modulation of light emission is at most about 10:1 to 20:1 since this depth is determined by the ratio between the light emission recombination times at light emission and non-light emission times.
Further, although the internal quantum efficiency (the ratio between the number of injected electrons and the number of generated photons) is very high, there exists the shortcoming that light could not effectively be output, which is a drawback common to such devices that emit spontaneous emission light. In general, this is due to the large refractive index of a semiconductor of the light emission active layer and because total reflection occurs in usual structures.